Electronic switching



P 7, 1 54 s. VAN MIERLO 2,688,661

ELECTRONIC SWITCHING Filed Jan. 5, 1951 3 She ets-Sheet l *0 *-o I L. cm40 LINE. Cmcurr $0 UR c 5 0;

// POL 565 luvanaroa. A I$LA5 VAN M ER -O Attorney P 7, 1954 s. VANMIERLO 2,688,661

ELECTRONIC SWITCHING Filed an- 1951 3 SheetsSheet s I nvenior STAN/SD15MN N/EILO Attorney Patented Sept. 7, 1954 2,688,661 ELECTRONIC SWITCHINGStanislas Van Mierlo, Antwerp,

Belgium, assignor to International Standard Electric Corporation, NewYork, N. Y., a corporation of Delaware Application January 5, 1951,Serial No. 204,654

Claims priority, application France January 6, 1950 7 Claims. 1

The present invention relates to improvements in electronic switchingsystems and particularly to commutation systems in which one or severalcircuits taken from a plurality of circuits are electronically connectedrespectively to one or several channels of a multiplex junction.

In switching systems used in automatic telephony the line circuits ofthe subscribers of the same group can be connected, when thecorresponding subscriber calls, to one of the junctions common to thesubscribers of the group, as long as there remains a free junction, thenumber of the junctions being generally lower than the number ofsubscribers of the group. In such systems, the detection of new calls iseffected by electronic or electromechanical means, while the necessaryswitchings are generally made by mechanical or electromechanical means.It has already been suggested to replace the groups of junctions betweenthe different subscribers"- groups or between the diiferent parts insidea telephone exchange by multiplex junctions, the scanning of thediiferent subscriber lines or of the different junctions and theallocation of a channel of a multiplex junction to a subscriber or acircuit being made by means of electronic switches, for instance,utilising cathode ray tubes.

One of the objects of the present invention is to provide an electronicswitching system of the said type in which the test and the necessaryswitchings are made by purely electronic means.

According to one feature of the invention, an electronic switchingsystem comprises, in combination, a plurality of circuits associatedwith means adapted to characterise each one of the said circuits by acode, a multiplex junction, electronic connection means adapted toconnect one or several of the said circuits respectively to one orseveral channels of the said multiplex junction associated with registermeans adapted to register the code of one or several of the saidcircuits and to control the establishment of the connection between thesaid circuits the code of which has been registered and the saidmultiplex junction by the said electronic connection means.

According to one feature of the present invention, an automatictelephone system comprises, in combination, a plurality of subscriberlines connected to subscriber line circuits, means adapted tocharacterise each subscriber line circuit and the line circuitassociated with it by a code, a multiplex junction having a plurality ofchannels the number of channels of the said junction being lower thanthe number of said subscriber line circuits, means adapted tocharacterise a calling line by a modification of the electriccharacteristic of one of the points of the line circuit associated withmeans adapted to successively and periodically apply the codecharacteristic of each subscriber line to means sensitive to variationsof the electric characteris tic of a calling line, said means beingadapted to modify the electric characteristic of one of the points oftheir circuit each time that the code characteristic of a callingsubscriber line is transmitted to it, a plurality of register means,equal in number to the number of the channels of the said multiplexjunction, to which the subscriber code furthermore applied to the meanssensitive to variations of the calling line characteristic istransmitted, each one of the said register means being adapted toregister the code of a subscriber having caused the variation of theelectric characteristic of the means sensitive to variations of the.calling line characteristic, the said register means being associatedwith a directing device adapted to successively and periodically connecteach one of the lines the code of which has been registered to thecorresponding channel of the said multiplex junction.

According to another feature of the invention, in such systems asubscriber line circuit comprises in combination: a transformer theprimary winding of which is divided into two parts interconnected by abattery, two wires of the subscriber lines being connected to theterminals of the primary winding of said transformer one of theterminals of which is thus given a different potential, according as towhether the subscriber line is looped or not, the said potentialsrespectively characterising a calling line and a free line.

According to another feature of the present invention, means sensitiveto variations of potentials of the calling lines comprise incombination: a resistance common to all the line circuits associatedwith means for bringing the potential of one of the ends of the saidresistance to a fixed potential lying between the potentialcharacterising a calling line and the potential characterising a freeline, a plurality of rectifying cells, in equal number to the number ofgroup circuits, the said rectifying cells being respectively connectedbetween each one of the terminals of the line circuits the potential ofwhich is characteristic of a calling line and the second end of theresistance common to the whole line circuits. the conductive directionin which the said cells are connected being such that a current can onlyflow in the said common resistance when one or several lines of thegroup are calling, a network of rectifying cells the output terminals ofwhich are respectively connected to the terminals of said rectifyingcells connected to different circuits of the lines of the group, meansadapted to periodically and in a predetermined order apply the differentcombinations of positive and negative potentials to the input terminalsof said network of rectifying cells, the number of the differentcombinations being at least equal to the number of the subscriber linesof the group, the different combinations of positive and negativepotentials and the network of rectifying cells being chosen in such away that to a given combination of negative and positive potentials apredetermined line corresponds, which when calling allows a current toflow throughout the resistance common to all the subscriber lines of thegroup, the current coming from the other calling lines then beingabsorbed by the said network of rectifying cells, the time position ofthe potential variation on the terminals of the said resistance commonto all the lines of the group being characteristic of the calling line.

According to another feature of the invention, in such systems the codecharacterising each calling line is a binary code. 7

According to another feature of the invention, each one of the registermeans comprises, in combination, a proper number of cold cathode tubesassociated with means adapted to transmit, under the form ofcombinations of positive and negative potentials, respectively to eachone of the triggering electrodes of said cold cathode tubes, each one ofthe code elements of the code of the subscriber connected to the devicesensitive topotential variations of the different line circuits of thegroup, associated with means adapted to bring the said triggeringelectrodes to such a potential that the cold cathode tubes cannot firewhatever may be the potential combination which would furthermore beapplied to them, when no potential variations is transmitted by thecircuit sensitive to potential variations of the calling lines, the saidmeans being also adapted not to exert action on the potentials thecombination of which is characteristic of the subscriber whose line isunder scanning each time that the circuit sensitive to potentialvariations of a calling line modifies the potential on the terminals ofthe resistance common to all the line circuits, the value of thepotentials the combination of which characterises the subscriber codebeing chosen in a proper way so that the positive potentials cause thefiring of the corresponding cold cathode tubes.

According to another feature of the invention, each one of thesubscriber lines is connected to the multiplex junction by an electronicgate comprising two rectifying cells, oppositely poled, the saidelectronic gate allowing the passage of the modulated current from or tothe subscriber line each time that a current flows through the said twooppositely-poled rectifying cells.

According to another feature of the present invention, in such systemsthe distributing device comprises, in combination, a network ofrectifying cells the output terminals of which are respectivelyconnected to the points common to the two rectifying cells of eachelectronic gate of the lines of one group and on the input terminals ofwhich are applied positive and negative otential combinationscharacterising the code of each subscriber, the said network ofrectifying cells being provided in such a way that an output terminalcorresponds to each combination of positive and negative potentialapplied to the input terminals, and a current flows from said outputterminal throughout the two rectifying cells of the electronic gatewhich is connected to it, the other output terminals being then broughtto such a potential that no current flows in the rectifying cells of theelectronic gates which are connected to them, so as to place thesubscriber line, connected to the electronic gate, the two rectifyingcells of which are traversed by a current, in communication with themultiplex junction.

According to another feature of the invention, such systems comprisemeans adapted to successively and periodically transmit, under the formof positive and negative potential combinations, the subscriber codeswhich habe been registered by potential variations of the anodes of coldcathode tubes, to the input terminals of a network of rectifying cellsthe output terminals of which are connected to the electronic gates, soas to successively and periodically place each subscriber, the code ofwhich has been registered, in communication with the multiplex junction.

According to another feature of the invention, such systems comprisemeans adapted to transmit potential variations of each output terminalof said network of rectifying cells connected to the differentelectronic gates at the point of the corresponding line circuit thepotential variations of which are characteristic of a calling line, soas to modify the potential of said point of the line circuit as soon asthe said line is connected to said multiplex junction, and to suppressthe subsequent sending of impulses towards the register means andthrough the circuit sensitive to potential variations of the callingline and thus to avoid the registration of the subscriber code inanother register means.

Other objects, features and advantages of the present invention willclearly appear from the following description of an embodiment utilisingfeatures of thepresent invention, the said description being made inrelation with the annexed drawings in which:

Fig. 1 represents a plurality of subscriber line circuits, one of whichis shown in detail,

Fig. 2 represents a scanning circuit,

Fig. 3 represents a distributing .circuit,

Fig. 4 represents a register circuit,

Fig. 5 represents two impulse transformer circuits, one of which isshown in detail,

Fig. 6 represents an electronic distributor,

Fig. '7 represents diagrams of impulses.

In the detailed subscriber line circuit of Fig. l, the line wires 1 and2 are connected to terminals 3 and 4 of the primary winding oftransformer 5. The primary winding of transformer 5 is divided into twoparts 6 and I interconnected by a 48 volt battery 8. The positiveterminal of battery 8 and terminal 3 of the winding of transformer 5 areconnected to ground. Terminal 4 of the primary winding of transformer 5is connected to terminal 9 of the linecircuit by means of resistances l0and H. One of the terminals of the secondary winding of transformer 5 isconnected to ground, the other terminal i5 being connected by means ofcondenser H to terminal l3 of the line circuit. A condenser M isparallelly connected to the secondary winding of transformer 5. Point [6common to resistances and H is connected by means of :a circuitcomprising rectifying cells ll! and l8 and condenser Hi to terminal 24o'fthe line circuit. The rectifiers l1 and 18 and condenser J9 areconnectedin series, the rectifiers being adjacent the point 16 and poledso as to pass current .away from point I 6. Abattery 23 has its positiveterminal connected to ground and its negative terminal connected througha resistance 2! to the junction of rectifiers 11 and 1B. The resistance2! is shunted by a condenser 20. A resistance '22 is connected betweenthe negative terminal of the battery 23 and the junction betweenrectifier l8 and condenser (9. The subscriber station has beenschematically represented by a switch '25 which is opened when thesubscriber hangs "up his receiver. The rectangles A and B representother subscriber line circuits identical with that just described.

Fig. 2 represents a circuit adapted to detect the calls andto transmit,"for each new detected :call, a new series of impulses the time positionof which with respect to reference impulses is characteristic of the newcalling line. This circuit will be designated in-the followingdescription as scanning circuit. The output terminals -9 (Fig. 1) of thethree subscriber lines are respectively connected to terminals '26, 21and 28, each terminal being'connected through a rectifying cell, such as29, 30 and 3|, to one of the ends of resistance 32, the other end ofwhich is connected to the negative terminal of a 36 volt "battery 33.The junctionof resistance 32 and the rectifiers 29, 30, and 3| isconnected to an output terminal 39 which thus forms a common point forthese rectifiers and resistance. A network of rectifying cells isconnected'between ter- I -minals 25, '21 and 28 "and'terminals 35, 36,31 and 38. Thus, the terminal 26 is connected to the terminal 3'!through the rectifier 34 and to the terminal 35 through'the rectifier34'; terminal 2'! is connected to the terminal '31through the rectifier4| and to the terminal 36 through the rectifier 40; the terminal 28 isconnected to the terminal 35 through the rectifier 40' and to theterminal 38 through the rectifier 4|. To terminals 35, 36, 31 and 33 areconnected, respectively, pulse sources '35, 36', 31', and 38' whichproduce recurrent impulses the form and amplitude of which have beenindicated in Fig. 7. In'this figure the source which produces theimpulse is identified on the right'hand side with respect of each seriesof impulses.

In the following description, each subscriber will be designated'by thereference of the terminal of scanning circuit to which terminal '9 ofits line circuit is connected. When a subscriber calls, the switch 25 ofits station closes the circuit of battery'8. The potential of point *9tends to risefrom 48"volts to 24'V01ts. 'If subscriber 21 calls, itwill'b'e seen that acurrent would then tend to be establishedbetweenpoint 3 of its line circuit and ground, through resistance 32which would tend to cause output or common point 39 to rise to 24 volts.On the 'otherhand, terminal 2! is connected to rectifiers "4'0 and 4|,themselves respectivelyconnected to terminals 33 and 31. If at least oneof the terminals 36 and 3'1'isat a'negativepotential with respect to thepotential of point 9 of the callin line (-24'volts) no current will flowthrough rectifier 30, thecurrent 'coming'from point 90f the line circuitof-the calling line being absorbed towards terminals "36*an'd 31.The'current consequently can onlyflow from line 2T'to point 39 beingregularly repeated.

during time 43 .(Fig. 7.), during which terminals 36 and 31 are broughtto potential 0. Then there will beobtained on point 39, due to thevoltage drop in resistance 32, a positive impulse the form of which hasbeen represented in Fig. '7 on .line

39. It will also be seen that in the case in which lines 26 and 28 arecalling,:an impulse is obtained respectively .in times 42 and 44, theseimpulses Each one of the three subscribers is thus characterised by atwo element binary code. If there is conventionally designated by l .thecombination of potentials 0 volt and 48 volts respectively applied ontermina'ls 35 and 36 or on terminals 31 and 38, and by '0 the inversecombination, it will be seen that subscribers 26, 2! and 28 arecharacterised by codes 11, 01, 10.

In the considered embodiment, the lines are scanned 500 times persecond, each .line being scanned during 500 microseconds.

Fig. 3 represents an electronic distributor. The impulses produced at 39(Fig. 2) are transmitted to an impulse regenerating circuit 41 whichgives in its output an impulse of predetermined amplitude; in the caseconsidered, the impulses transmitted to terminal 46 are transformed into50 volt-positive impulses from 150 volts. Such an impulse regeneratingdevice may,

for instance, comprise a cold cathode tube to the control grid on whichis transmitted the impulse to be regenerated; the regenerated impulse isthen collected in the cathode circuit. The impulse obtained in theoutput of circuit 41 is transmitted by means of resistances 48 and 49,on the one hand to rectifying cells 50 and 5| and on the other hand toterminals 84 and 84 of the calling subscriber code register circuitwhich will be described in relation to Fig. 4. The

other terminals of the rectifying cells 50 and 5| are'on the other handconnected to terminals 52 and 53. 50 volt positive impulses from 150volts are transmitted 250 times per second to terminal 52 from source52', each impulse having a 2000 microsecond duration, i. e. the durationof the scanning for the total of the lines. 2,000 microseconds identicaldisplaced impulses are also transmitted to terminal 53 from source 53'.These impulses are respectively represented on lines 52 and 53 of Fig.'7. If there is assumed that an impulse characteristic of a calling lineis transmitted to terminal 46, it is transformed by the regeneratingcircuit 41 into a 50 volt impulse from 150 volts, and during all thisim- "pulse (500 microseconds) point 54 is brought to l00 volts. Ifduring the calling lines scanning cycle, during which this impulse takesplace, ter- 'minal 52 is at a potential l00 volts, terminal 53 beingthen at potential -l50 volts, a current will flow between point 54 andterminal 53 through resistance 49 and the rectifying cell 5|; terminal84 is then brought -to a potential near l50 volts. Point 54 and terminal52 being brought to the same potential, volts, terminal 64 is broughtduring the impulse to potential 100 volts. If the impulse characterisinga calling line takes place during the following cycle, during whichterminal '52 is at l50 volt potential and terminal 53 at 100 voltpotential, terminal 64 would be maintained at a potential near l50 voltsand terminal 84 at a 100 volt potential. When no impulse characterisinga calling line is transmitted to terminal 46, point -54-is at l50 voltpotential and due to the sense -in which rectifying cells'50 and 5| areconnected, terminals6'4 and-84 are held at volt potenti'al whatever maybe the potential of terminals 52 and 53.

Fig. 4 represents a calling subscriber code register circuit. Itcomprises two circuits 60 and 80 each one comprising two cold cathodetubes, i. e. a cold cathode tube per one code element. The two circuitsare identical and only circuit 60 will be described in detail. In bothcases, elements playing an identical part are shown by means ofreference number having the same unit figure. The anode of each of thecold cathode tubes 6i and 62 is connected to the ground through aresistance such as 05, and each cathode is connected to negativeterminal I of a 200 volt battery through a resistance, such as 66, andthe common element 61 which comprises a resistance in parallel with acondenser.

I The anodes of cold cathode tubes BI and 8| are furthermorerespectively connected through resistances 58 and 88 and rectifyingcells 69 and 89, to terminal II. The anodes of cold cathode tubes 62 and82 are identically connected by means of resistances I3 and 93 andrectifying cells I4 and 94 to terminal I2. The terminals II and I2 areconnected to ground, respectively, through resistances I0 and 90. Thepoints common to elements 68 and 09, on the one hand, and to elements I3and I4, on the other hand, are connected to terminal I5 by means ofresistances, such as I8, while the points common to elements 80 and 0-0,on the one hand, and to elements 93 and 94, on the other hand, areconnected to terminal 95 through resistances, such as 93. Terminal 64(Fig. 3) is connected to each one of the triggering electrodes of coldcathode tubes BI and 62 by means of rectifying cells, such as 16, whileterminal 84 (Fig. 3) is connected by means of rectifying cells, such as35, to each one of the triggering electrodes of cold cathode tubes 8|and 82. The triggering electrodes of tubes BI and 8I are respectivelyconnected by means of resistances 63 and 83 to terminal IOI, while thetriggering electrodes of cold cathode tubes 62 and 82 are respectivelyconnected by means of resistances TI and 9'! to terminal I02.

Terminals I5 and 95 are connected to the output terminals of asymmetrical multivibrator circuit which has been represented byschematic device I9. Such devices are well known in the art and it ispossible to connect terminals I5 and f 95 in the anode circuit of eachone of the two triodes constituting the multivibrator so as to obtain onone of the two terminals a negative potential, for instance, the otherterminal then being at the earth potential of the device on which thepositive terminal of the high tension voltage is connected. Thefrequency of the multivibrator circuit I9 is adjusted at 10,000 cyclesper second and the form of the impulses transmitted to terminals I5 and35 has been represented in Fig. 7. Impulses shaped as those transmittedto terminals 35 and 31 (Fig. 2) are respectively transmitted toterminals IOI and I02 of the register circuit (Fig. 4) from impulsesources MI and I02, the pulses being indicated on lines WI and I02 ofFig. '7. The amplitude of these impulses lies between 100 volts and 150volts.

Normally, all the cold cathode tubes of the different circuits are cutout, the potential applied on the cathode (-200 volts with respect tothe anode) being insuificient to cause firing. In order for one of thecold cathode tubes to ionize, it is necessary that its triggeringelectrode be brought to -100 volts. If we, for instance, consider thecase of cold cathode tube 0i, it will be seen that its triggeringelectrode can only be brought to -100 volts, when terminal 6 3 of thedistributing device, represented on Fig. 3, and terminal IOI aresimultaneously brought to l00 volt potential. If we assume, that line 2i(Fig. 2) is calling, an impulse of 500 microseconds is transmitted frompoint 39 (Fig. 2) by the distributing circuit (Fig. 3) to one of theterminals 64 and 04, according to the potential combination applied onterminals 52 and 53. It is assumed that no limitation results from thisfact, that when the impulse is transmitted to the distributing circuit,terminal 52 is at 100 volt potential and terminal 53 at l voltpotential, as it is represented on Fig. '7. The impulse varying from-l50 volts to 50 volts is then transmitted to terminal 64 as an impulseof l00 volts, and its time position, with respect to impulsestransmitted to terminals 35, 30, 31 and 38 of the scanning circuit (Fig.2), is characteristic of the calling line. In the particular consideredcase, terminal IOI is at 150 volt potential and terminal I02 is at l00volt potential, while terminal 64 is at volt potential. In this casecold cathode tube 62, the triggering electrode of which is brought to-100 volts, fires, while cold cathode tube 6|, the triggering electrodeof which is brought to the potential of terminal WI volts) does notfire. The anode potential of tube BI thus remains at potential 0, theanode potential of tube 62 becomes negative due to the voltage drop inresistance 05. Tubes 0| and 32 of the second circuit remain unfired dueto the fact that terminal 84 is held at l50 volts. As a matter of fact,terminal IOI being at 150 volt potential, no current is established inresistance 83 and the rectifying cell 90 connected to the triggeringelectrode of tube 8| which is also held at -l50 volt potential, while acurrent is established between terminal I02 and terminal 04 throughresistance 91 and rectifying cell 90 connected to the triggeringelectrode of cold cathode tube 02 which is thus brought to l50 voltpotential. The resistances in the elements 51 and 81 connected in thecathode circuit are provided so as to cause a potential drop when one ormore of the tubes of the circuit are fired, such that the cathodepotential is no longer sufiiciently low to permit the firing of cut-outtubes, even when the potential of the triggering electrode of thesetubes is brought to l00 volt potential. On the other hand, thecondensers of elements 07 and 01 delay the rise in potential of thecathode circuit when two tubes are supposed to fire simultaneously andone tube fires a little ahead of the other, so that the other tube isnot prevented from firing. Furthermore, as will be described inconnection with the electronic switch represented on Fig. 6, means isprovided adapted to suppress the sending of the impulse the timeposition of which is characteristic of the calling line as soon as thecode of this line has been registered, so as to prevent the registeringof the calling line code in the following circuit, if free, when thedistributing device, represented in Fig. 3, will transmit impulsesproduced at 39 (Fig. 2) to terminal 84 (Figs. 3 and 4) during the secondcycle of subscriber line scanning.

Fig. 5 represents two fiip-fiop circuits each utilising two triodes I03and I04. Only one circuit C is shown in detail, the other beingrepresented by the rectangleD. The grid of triode I03 of fiip-fiopcircuit C is connected through a battery I05 to terminal II, (Fig. 4)the potential difference between the terminals of the battery and thedirection in which it is connected being such that triode I 03 isconductive when terminal II is at potential and that the triode isblocked when terminal II is at a negative potential which it is whencold cathode tube 0| is conducting. The cathodes of triodes I03 and I04are connected to the negative terminal of a 200 volt battery throughresistance IN, the anodes being connected to earth respectively throughresistances I03 and I04. When terminal II is at a positive potential (0volt), triode I03 is conductive and the anode of triode I03 is at anegative potential with respect to ground. In the embodiment underconsideration, the value of resistance I03 is chosen in such a way thatthe anode potential is 48 volts when the triode is conductive. A currentthen flows in resistance I01, the cathode potential increases and blockstriode I04, the grid of which is connected to a suitable point of thecommon cathode resistance. The anode of triode I04 is then brought toground potential.

Terminals II and I2 are connected to terminals II and I2 of two circuitsC and D which are identical. If we assume, as it has been shown the caseabove, that the code of subscriber 2'! (Fig. 2) is recorded in circuit60, the anode of tube BI is at the earth potential and the anode of tube62 is at a negative potential with respect to earth, for instance -10volts.

As long as terminal I5 is at the earth potential (0 volt), the anodepotential of tube 6| has no influence on the potential of terminal I Idue to the direction in which rectifier 09 is connected. Also in thiscase the anode potential of tube 62 has no influence on the potential ofterminal I2. When terminal I5 is brought to a negative potential, acurrent can be established between the anodes brought to a negativepotential and the earth through resistances I0 or 90. For instance, inthe case under consideration the anode of tube 62 is brought to anegative potential with respect to the earth and a current can beestablished through resistance I3, rectifying cell I4 and resistance 90bringing the grid potential of triode I03 in the flip-flop circuit D toa negative poten-' tial with respect to the cathode. Triode I03 of thiscircuit D is then blocked and its anode is brought to earth potentialwhile the anode of tube I04 receives a -48 volt potential, according tothe above mentioned operations. If we designate by I 00 and I09 theoutput terminals connected to the anodes of tubes I03 and I04 of theflip-flop circuit C connected to terminal II and by H0 and III theoutput terminals of the flipflop circuit D the input terminal of whichis connected to terminal 72, it will be seen that we will obtain, in thecase in which the code of sub scriber 2! is recorded in circuit 00, -48volt,

'0 volt, 0 volt, -48 volt potentials respectively on terminals I08, I09,H0 and III, each time terminal I5 is brought to a negative potentialwith respect to the earth. We also assume that circuit 80 is free andthat consequently the anodes of the cold cathode tubes of this case areat 0 volt potential. When the potential of terminal I5 is at 0 potentialand therefore the potentials of the anodes of the different cold cathodetubes of circuit 60 have no longer an influence on the potentials ofterminals II and I2, terminal 95 is brought to a negative potential withrespect to earth and no current flows inthe anode of the said tubestowards the earth through resistances I0 and 90, connected to terminalsII and I2. It

is easy to see that in this case terminals I00, I09, I I0 and III arerespectively brought to 48 volt, 0 volt, 48 volt, 0 volt potentials.Terminals I5 and are alternatively negative and positive at 10,000 timesper second and the subscriber code registered in circuit 60 will bereproduced 10,000 times per second on terminals I08, I09, H0 and I I I,each time during 50 microseconds, while the code corresponding with nosubscriber, as circuit 80 is free, is transmitted 10,000 times persecond between the period during which the code registered in circuit 60is transmitted.

In the particular embodiment considered it has not been envisaged tolimit the system to one comprising three lines and utilising a twocircuit register; it is easy to see that in a system compris ingsubscriber lines it is possible to utilise a register having 16circuits, for instance, each circuit comprising seven cold cathode tubesto register a seven element code; in this case, the symmetricalmultivibrator utilised to successively distribute the code of eachsubscriber to terminals I08, I09, H0 and III, would be replaced, forinstance, by a distributing circuit utilising rectifying cell networks,said circuit being adapted to connect each one of the 16 circuitssuccessively, 10,000 times per second and each time during 6microseconds, to a set of '7 terminals playing a part identical to theone played by terminals II and I2 (Fig. 5).

Fig. 6 represents the circuit enabling the subscriber whose code isregistered under the form of a potential combination on terminals I08,I09, I I 0 and I I I, to be connected to the channel of the multiplexjunction. The channel of the multiplex junction is indicated at I 25 andthe terminals at the left of Fig. 6 are connected respectively to thoseat the upper right of Fig. 1, so that each line circuit has two leadsconnected to the channel. In order that the current, outgoing from theline A (Fig. l.) connected for instance to terminal I I3 (subscriber26), will pass through the electronic gate composed of rectifying cellsH6 and III, it is necessary that a current is made to flow between theearth and point H8, held at 48 volt potential by battery H9, throughresistances I20 and I2I, rectifying cells H6 and III, and resistanceI22. This can only take place when neither of terminals I 09 and III arepositive. This will happen when terminals I08 and I I0 have 0 voltpotential applied to them and terminals I08 and III have a negativepotential (-43 volts) applied to them. If one of terminals I09, III, orboth at the same time, were brought to a positive potential, a currentwould be established between the terminal brought to the positivepotential (I00 for instance) and point I I0 through resistance I 22 andrectifying cell I23, thus bringing the potential of point I24 to near 0and suppressing the current through cells H0 and III. In the embodimentconsidered in connection with the previous figures, the code of thesubscriber the line circuit circuit of which is connected to terminal ZI(Fig. 2) is transmitted, under the form of a potential combination (-48volts, 0 volt, 0 volt, 48 volts respectively) to terminals I09, I00, H0and III, 10,000 times per second, and each time during 50 microseconds.Each time that this code is transmitted the subscriber line connected toterminal IM from terminal I3 of Fig. 1 is connected with the inputterminal I25 of the multiplex junction. Between the periods during whichthe line connected to terminal I I I is connected with the multiplexjunction, the potential combination --48 volts,

volt, -48 volts, 0 volt is transmitted to ter minals I08, I09, III! andIII, if we assume that circuit 80 is free. It is easy to see that, inthis instance, no line is connected with the multiplex junction. In thecase in which the code of another subscriber has been registered incircuit 80 (Fig. 4) this code would be transmitted under the form of apotential combination to terminals I08, I09, III! and III, instead ofthe code characterising the non-busy condition of circuit 80, and thissubscriber would be connected with the multiplex junction betweenperiods during which line 21 is connected.

The terminal corresponding to 24 of each line circuit is connected tothe common point of the two rectifying cells constituting the electronicgate between the terminal corresponding to I3 and the multiplex junctionI25 of this line. For instance, point 24 of line 21 is connected topoint I26. As soon as point I6 of the line circuit is brought to -24volts, the code of the line is then registered, as has been aboveexplained, on the cold cathode tubes of one of the circuits of thecalling subscriber code register. This code is then applied 10,000 timesper second to terminals I08, I09, II!) and III. Each time that the codeis applied, a current flows between point I I8 and the earth throughrectifying cells I21 and I28 and resistances I20 and I30. Point I26 isthus brought to a negative potential with respect to -24 volts, andcondenser 20 (Fig. 1) is charged during all the impulse. Between everytwo of the periods during which the line is connected to the multiplexjunction I25, condenser 20 is discharged through resistance 2| keepingthe end of resistance 2i, connected to rectifying cell H, at a negativepotential with respect to the potential of point I6 (-24 volts). PointI6 is thus brought to a potential near -36 volts. This potential fallprevents current flowing from point 9 of the calling line towardsbattery 33 (Fig. 2) when the line is scanned a second time by thescanning circuit (Fig. 2), thus preventing another registration of thecalling subscriber code in the second circuit of the register circuit(Fig. 4) during the second period of line scanning.

A system has been described comprising only three subscriber lines andin which the scanning circuit (Fig. 2), the distributing circuit (Fig.3), and the connection circiut (Fig. 6) utilise rectifying cellnetworks. It is clear for those skilled in the art that electroniccircuits, for instance utilising cathode ray tubes, such as thosedescribed in French Patent No. 930,641, corresponding to United StatesPatent No. 2,584,987, issued in February 12, 1952, to E. M. Deloraine,may be utilised either in the scanning circuit, or in the circuits inwhich it is necessary to transmit an impulse to a predetermined circuitselected among a plurality of circuits. In the same way a certain numberof circuits, such as the flip-flop circuit represented in Fig. 5, thesymmetrical multivibrator circuit having the reference I9 (Fig. 4) andthe impulse regenerating circuit 41 (Fig. 3), could be realised indifferent ways well known in the art.

More generally the circuits or elements utilised in the system describedcan be replaced by circuits or organs playing an identical functionwithout departing from the scope of the present invention.

I claim:

1. An electronic switching system comprising a plurality of linecircuits, a resistor, separate means for connecting each of said linecircuits to a common point on one end of said resistor, said means eachincluding a uni-directional current-carrying device, said devices allbeing poled in the same direction, a plurality of conductors, meansincluding uni-directional current-carrying devices for connecting eachof said line circuits to a predetermined different combination of saidconductors, said last-mentioned devices being poled in the samedirection with respect to said lines as said first-mentioned devices,sources of voltage pulse trains having difierent pulse characteristics,there being one for each of said conductors, means for connecting saidsources between the other end of said resistor and said conductors,means in each of said line circuits for normally maintaining a potentialdifference between said circuit and the other end of said resistor, suchas to prevent current flow through said resistor, means in each of saidline circuits responsive to a change of condition of said line circuitfor altering said potential difierence so as to permit current flowthrough said resistor when simultaneous pulses on the conductorsconnected thereto block current flow between said conductors and saidline circuit, whereby the potential on said common point will be alteredfor the duration of said simultaneous pulses, thus producing a voltagepulse whose time position will be characteristic of the line circuit thecondition of which has been changed, an output channel, a first gatingnetwork connected between all of said line circuits and said channel andnormally blocking current flow between said circuits and said channel,registering means connected to said common point for registering thetime position of a pulse appearing on said common point and having anoutput connected'to said gating network, and means controlled by saidregistering means for causing said gating network to permit current flowbetween said chan nel and the line circuit the time position of whichhas been registered in said registering means.

2. An electronic switching system, as defined in claim 1, in which thesources of pulse trains connected to the conductors are arranged toproduce simultaneous pulses on the combination of conductors connectedto a given line at a time position in a repetitive cycle which isdifierent from the time position in said cycle at which simultaneouspulses appear on the combination of said conductors connected to anyother of said lines.

3. An electronic switching system, as defined in claim 1, in which theregistering means comprises a plurality of gas discharge tubes and meansfor biasing difierent combinations of said tubes for each time position,whereby an input pulse from the common point at a particular timeposition will fire a particular combination of said tubes, the outputcircuits of said tubes being connected to said gating network.

4. An electronic switching system, as defined in claim 3, in which thegating network comprises a connection from each line to the channel,said connection including two oppositelypoled, unidirectional,current-carrying devices, means for normally biasing the junction pointof said devices so as to prevent a signal from passing through saiddevices to said channel and means connected to the registering means andcontrolled by the setting thereof for removing the bias at predeterminedrepetitive times for permitting a signal to pass to said channel.

5. An electronic switching system, as defined in claim 1, in which thereare a plurality of registering means, and further comprising adistributor connected between the common point and said registeringmeans, means for causing said distributor to connect said common pointto said registering means in succession, and Switching means forefiectively connecting said registering means successively to the gatingnetwork.

6. An electronic switching system, as defined in claim 5, in which theswitching means comprises a second gating network connected to theoutputs of the plurality of registering means, and means for blockingthe outputs successively in a repetitive cycle.

7. An electronic switching system, as defined in claim 6, furthercomprising a condenser network in each line circuit, connected to thefirst gating circuit, means for lowering the potential of the linecircuit so as to prevent current flow through the resistor when saidcondenser network is charged, said condenser network being connected tosaid first gating network, and means in said gating network for chargingsaid condenser network during a time immediately following the timeduring which current is permitted to flow between the channel and saidline circuit.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,133,415 Baker et a1 Oct. 18, 1938 2,152,889 JedrychowskiApr. 4, 1939 2,563,589 Den Hertog Aug. 7, 1951 2,580,093 Hersey Dec. 25,1951 2,583,711 Scowen Jan. 29, 1952

